1. Field of the Invention
The present invention relates to an image forming method and apparatus, and more particularly, to droplet deposition control technology suitable for reducing deterioration of image quality caused by ejection failure of a droplet ejection port (nozzle) of an inkjet recording apparatus or other image forming apparatus comprising an ejection head having a nozzle row in which a plurality of nozzles are arranged through a length corresponding to the entire width of a recording medium.
2. Description of the Related Art
In an inkjet printer, for a variety of reasons, a situation may occur in which it becomes impossible to eject ink from a nozzle. If a particular nozzle of the nozzle group suffers an ejection failure, then dots that should originally have been formed on the recording medium by that nozzle are missing, and an unintended stripe-shaped defect (stripe non-uniformity or “banding”) is thereby produced in the image formed on the recording medium. This banding is extremely conspicuous.
In particular, in the case of a device configuration that completes printing by means of a single sub-scanning operation, using a line-type recording head in which a plurality of nozzles are arranged, unlike a shuttle (multi) scanning system, it is difficult to cover the droplet deposition position of a nozzle suffering an ejection failure, by means of another nozzle (in other words, a so-called “shingling” operation), and banding non-uniformity due to the nozzle suffering the ejection failure is highly notable, leading to serious deterioration in image quality. Japanese Patent Application Publication Nos. 2002-19101 and 2002-67297 disclose methods by which, if any of the nozzles in the print head is suffering an ejection failure, deterioration in image quality thereby caused is made to be inconspicuous.
Japanese Patent Application Publication No. 2002-19101 discloses the supplement of dots by means of a nozzle on a head of another color, instead of the nozzle that has become unable to perform recording due to an ejection failure. For example, a supplementary droplet ejection is made for the position of an ejection failure in a cyan head, by means of a nozzle on a magenta head.
Japanese Patent Application Publication No. 2002-67297 discloses a method whereby a large quantity of a printing-property-improving ink is deposited in the area of a deposition failure and the vicinity thereof so that the ink surrounding (neighboring) the line to have been printed by the nozzle suffering an ejection failure is drawn towards the defective area, thereby reducing the perceptibility of banding.
The supplementary (corrective) methods disclosed Japanese Patent Application Publication Nos. 2002-19101 and 2002-67297, however, indicate measures adopted after it has been identified by a method of some kind that a nozzle is suffering an ejection failure. In other words, they incorporate a step for “detection of ejection failures”, which is not required directly for printing, and therefore efficiency is poor.